The practice of reducing manganese ore with solid fuels such as coal or coke has generally been limited to two techniques. In the first method a mixture of ground ore and solid fuel is fed into a controlled atmosphere and temperature zone of an indirectly fired kiln. The kiln is rotated to provide for the necessary heat transfer and gas contact throughout the ore bed. Due to time limitations on the period for reduction of the ore, it is necessary to use ground ore in this process. In the second method ground ore and solid fuel are pelletized or compacted and then heated in a substantially inert atmosphere. The pellets are usually carried through the heating zone on a moving belt or grating, and the product is normally sintered.
These conventional techniques involve several undesirable features. Fuel efficiency is generally poor as a result of the heat losses inherent in indirect firing. In addition, it is necessary to grind the raw ore prior to reduction, and raw manganese ore is roughly twice as difficult to grind as reduced ore. A further drawback is the high capital investment and maintenance cost of the equipment involved.
A method for the direct reduction of manganese ore in a bed, or pile, has been disclosed in my U.S. Pat. No. 3,375,097. However, this method involves the use of relatively large quantities of natural gas which is in increasingly short supply. In view of the disadvantages of this and other previous ore reduction methods, it is desirable to develop a practical, economical and energy efficient process for reducing manganese ore with solid fuel.